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Expanding the Class D Conversation: How Would You Characterize Their Differences?

Expanding the Class D Conversation: How Would You Characterize Their Differences?

I'm currently trialing the NAD M23 (1st gen. Eigentakt-based), and I find it intriguing enough to want to understand it better — which means understanding the broader sonic landscape of class D. So I'm crowd-sourcing.

In a recent exchange, the estimable Ralph Karsten (Atma-Sphere Music Systems) made two comments that stopped me cold. For those who missed it, here's what he said:

"IME, class D amps vary in sound more than tube amps, which is to say, quite a lot."

"IMO there is a bigger difference between various class D amps than you hear between various tube amps. IOW just because you heard one class D amp says nothing about how the next one might sound."

Link: https://forum.audiogon.com/posts/2885828

As I think through this more carefully, these are genuinely important claims. My own experience with tube amps confirms that they produce audibly distinct characters across topologies and designs. If Ralph is right and class D exceeds that range, then generalizing from one class D experience to another is even more hazardous than I assumed.

One specific question for Audiogon members:

If you have a Class D amp or have compared class D amplifiers, how would you describe their character(s)?

Here are some criteria I use:

  1. Frequency balance — Is the tonal response even across bass, mids, and treble, or does it favor certain regions?
  2. High-frequency texture — Are the highs extended and smooth, or edgy, grainy, and fatiguing?
  3. Bass definition — Is the low end tight and articulate, or loose and bloated?
  4. Midrange character — Does the midrange feel present and natural, or recessed and thin?
  5. Transient speed — Does the amp respond quickly to dynamic attacks, or does it sound sluggish and rounded?
  6. Dynamic range — Does it scale convincingly from quiet passages to loud ones, or compress the difference?
  7. Soundstage width and depth — Does it create a convincing three-dimensional image, or sound flat and narrow?
  8. Image specificity — Are instruments and voices placed precisely, or do they blur and wander?
  9. Background noise floor — Is the silence between notes actually silent, or is there grain, haze, or hash?
  10. Long-term listenability — After an extended session, do you want to keep listening, or has something been quietly fatiguing you?

If you can include relevant system context — room, speakers, preamp — please do. Those variables will help me interpret what the amp itself is contributing.

I'm less interested in rankings than in understanding what Ralph mentioned, namely the [vast] range of sonic signatures class D is capable of. Eigentakt, Hypex, Pascal, Purifi, GaN-based, etc. — all fair game.

Price is no constraint here — I'm interested in the full range of what's out there.

hilde45
hilde45's avatar
hilde45 OP
5,997 posts
 

You’re the only person Ive run across that is saying the AGD sound isnt "Tube like".

How many was that, exactly? Now you’ve met someone, so more data for you.

So...my assessment of the AGD -- which I praised quite highly, so stay calm -- came from about 10 days of intensive audition of the Audion III monoblocks and running a careful, documented comparison against my XA-25 — and before that, against a Hypex-based NAD M23 — in my own system. Not from YouTube. Direct experience and systematic listening ought to count for something, even against a broad consensus. Systems vary enormously, and my ears in my room are the most relevant data I have. This is a forum, too, so keep some perspective.

As for methodology: buying and flipping if disappointed works for some people, and that’s fine. But not everyone has the budget or appetite for that kind of churn, and careful research before purchasing isn’t a character flaw — it’s a different approach with its own value. My documentation of these comparisons has been useful to others here, or so I’ve been told. If you tried the number of amps I’ve had, you’d be out a lot of coin. Maybe you have it to spend. Good for you. 

On the SIT-3: my posts reflect genuine first-hand listening experience. The amp is still available used, figures prominently in the review literature, and remains a live reference point for people considering purchases in this range. That makes it worth discussing regardless of how long it’s been on the market.

As for post count: the number of posts I have says nothing about the validity of any particular claim. Pointing to one gap in product knowledge and implying it casts doubt on everything else I’ve written is a hasty generalization. Questions and documented comparisons aren’t signs of inadequate homework — they’re how a certain kind of careful consumer operates. If that approach doesn’t suit you, my posts are easy enough to skip. 

atmasphere's avatar
atmasphere
12,404 posts
 

Can you also tell us what the 11 secret ingredients are to making KFC Chicken while you're giving away the blueprint to your amps??

@riaa_award_collectors_on_facebook 

Wait-wut? There are secret ingredients?? How do you know there are 11? Way above my pay grade

The comparisons that have always been made between AGD and Ralph's versions by people that have tried both is that AGD of the 2 is the one thats "Tube Like" and that Ralphs has more Grunt and Growl to it like Solid State.

I've heard the exact opposite. Take a look at our customer feedback page and you'll see what I mean. 

hilde45's avatar
hilde45 OP
5,997 posts
 

Regarding the comparison, well, it’s hard to find direct head-to-head comparisons. When I looked, I found these:

The Future Audiophile review of the Atma-Sphere Class D mentions the AGD Tempo di GaN as the most natural comparison point, noting the AGD has more power but that Atma-Sphere has a longer company track record. That same reviewer noted that their publisher had compared the AGD to a Pass Labs XA-25 and found them "quite comparable." This contrasts a bit with my own experience, but there you go.

The What’s Best Forum had one poster who had owned the Atma-Sphere Class D monos, AGD Duets, and Orchard Audio monos on separate occasions ranked them: Orchard first, AGD second, Atma-Sphere third. He said all three were competent and he’d be happy with any of them.

About the "tube" sound, the characterizations I could find are actually mixed and system-dependent. A Hi-Fi+ reviewer found the Atma-Sphere Class D surprisingly tube-like, remarking that Ralph had managed to "transport the classic Atma-Sphere OTL presentation to a Class D amplifier." 

This is a paltry list of comparisons, really. And there are lots of other comments on either amp and others out there. (I do not find evidence that AGD is definitively "more tube-like" than Atmasphere’s implementation, and I have not tried it for myself. And tube-like is just one criterion which is not all that important for many people, let's be honest.) Reviewers and forum members disagree, findings are system-dependent, so all I have tried to do here is offer my own first-hand experience -- laying out my system, my tastes, and my methods of comparison -- to offer one more data point.

bolong
962 posts
 

In my system running Audion mk3's fed by the Primaluna Evo 400 preamp (with Mullard NOS rectifier tubes and now Apos Ray 12au7's as signal tubes) the sound is not so much warm as it is "silky."

What still bothers me most about amps nowadays is that the volume control steps are too coarse.

devinplombier
1,650 posts
 

I saw the first post of this thread back in February, and I stopped reading when I saw

NAD

Which was unfortunate, because this looks like an excellent thread! Now I'm gonna have to go back and read the rest 🙂

 

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